U.S. patent number 6,914,802 [Application Number 10/163,059] was granted by the patent office on 2005-07-05 for microelectronic photonic structure and device and method of forming the same.
This patent grant is currently assigned to Axon Technologies Corporation. Invention is credited to Michael N. Kozicki.
United States Patent |
6,914,802 |
Kozicki |
July 5, 2005 |
Microelectronic photonic structure and device and method of forming
the same
Abstract
A microelectronic photonic structure and a device and a system
including the structure are disclosed. The photonic structure
includes an ion conductor and a plurality of electrodes. Optical
properties of the structure are altered by applying energy across
the electrodes.
Inventors: |
Kozicki; Michael N. (Phoenix,
AZ) |
Assignee: |
Axon Technologies Corporation
(Scottsdale, AZ)
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Family
ID: |
27537522 |
Appl.
No.: |
10/163,059 |
Filed: |
June 4, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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118276 |
Apr 8, 2002 |
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951882 |
Sep 10, 2001 |
6635914 |
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502915 |
Feb 11, 2000 |
6487106 |
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Current U.S.
Class: |
365/153; 257/3;
257/4; 257/E27.071; 257/E27.004 |
Current CPC
Class: |
G11C
11/5614 (20130101); H01L 27/24 (20130101); H01L
45/144 (20130101); H01L 45/143 (20130101); G11C
11/34 (20130101); G02F 1/155 (20130101); H01L
45/1266 (20130101); H01L 45/1226 (20130101); G11C
13/0011 (20130101); H01L 45/148 (20130101); H01L
45/146 (20130101); H01L 45/142 (20130101); H01L
27/101 (20130101); B82Y 10/00 (20130101); H01L
45/085 (20130101); H01L 45/145 (20130101); G11C
2207/104 (20130101); G11C 13/04 (20130101) |
Current International
Class: |
G02F
1/155 (20060101); G11C 16/02 (20060101); G02F
1/15 (20060101); G11C 11/34 (20060101); G11C
11/56 (20060101); H01L 27/10 (20060101); H01L
27/24 (20060101); G02F 1/01 (20060101); G11C
13/02 (20060101); G11C 011/00 () |
Field of
Search: |
;365/153
;257/3,4,296,508 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 434 359 |
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Jun 1991 |
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EP |
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0 434 359 |
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Jun 1991 |
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EP |
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Primary Examiner: Dinh; Son T.
Attorney, Agent or Firm: Snell & Wilmer L.L.P.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a CIP of U.S. patent application Ser. No.
09/502,915, entitled PROGRAMMABLE MICROELECTRONIC DEVICES AND
METHODS OF FORMING AND PROGRAMMING SAME, filed Feb 11, 2000 now
U.S. Pat. No. 6,487,106; and is a CIP of U.S. patent application
Ser. No. 09/951,882, entitled MICROELECTRONIC PROGRAMMABLE DEVICE
AND METHODS OF FORMING AND PROGRAMMING THE SAME, filed Sep. 10,
2001 now U.S. Pat. No. 6,635,914, and is a CIP of; United States
Patent Application Serial No. 10/118,276, entitled MICROELECTRONIC
DEVICE, STRUCTURE, AND SYSTEM, INCLUDING A MEMORY STRUCTURE HAVING
A VARIABLE PROGRAMMABLE PROPERTY AND METHOD OF FORMING THE SAME,
filed Apr. 8, 2002; and claims benefit of U.S. Patent Application
Serial No. 60/298,496, entitled OPTICAL DEVICES BASED ON
PROGRAMMABLE METALLIZATION CELL TECHNOLOGY, filed Jun. 5, 2001; and
claims benefit of U.S. Patent Application Serial No. 60/368,579,
entitled FAST OPTICAL ROUTERS BASED ON PROGRAMMABLE METALLIZATION
CELL TECHNOLOGY, filed Mar. 29, 2002.
Claims
I claim:
1. A photonic device comprising: an ion conductor formed of a solid
solution containing a first conductive substance; a first electrode
comprising a second conductive substance, wherein said first and
said second conductive substances comprised the same material; and
a second electrode.
2. The photonic device of claim 1, wherein said ion conductor is
formed of a solid solution of a chalcogenide material and a
metal.
3. The photonic device of claim 2, wherein said metal is selected
from the group consisting of silver, copper, and zinc.
4. The photonic device of claim 1, further comprising a barrier
material between said ion conductor and at least one of said first
and said second electrodes.
5. The photonic device of claim 4, wherein said barrier layer
comprises a conductive material.
6. The photonic device 4, wherein said barrier layer comprises an
insulating material.
7. The photonic device of claim 4, wherein said barrier layer
comprises a material selected from the group consisting of Ag.sub.x
O, Ag.sub.x S, Ag.sub.x Se, Ag.sub.x Te, where x 2, Ag.sub.y I,
where y 1, CuI.sub.2, CuO, CuS, CuSe, CuTe, GeO.sub.2,SiO.sub.2,
Ge.sub.z S.sub.1-z, Ge.sub.z Se.sub.1-z, Ge.sub.z Te.sub.1-z, where
z is greater than or equal to about 0.33, and combinations
thereof.
8. The photonic device of claim 1, wherein said first electrode
comprises excess silver.
9. The photonic device of claim 1, wherein said ion conductor
comprises a solid solution selected from the group consisting of
As.sub.x S.sub.1-x --Ag, Ge.sub.x Se.sub.1-x --Ag, Ge.sub.x
S.sub.1-x --Ag, As.sub.x S.sub.1-x --Cu, Ge.sub.x Se.sub.1-x --Cu,
Ge.sub.x S.sub.1-x --Cu, Ge.sub.x Te.sub.1-x --Ag and combinations
thereof, where x ranges from about 0.1 to about 0.5.
10. The photonic device of claim 1, wherein said ion conductor
comprises a glass having a composition of Ge.sub.0.17 Se.sub.0.83
to Ge.sub.0.25 Se.sub.0.75.
11. The photonic device of claim 1, wherein said ion conductor
comprises up to about 67 atomic percent silver.
12. The photonic device of claim 1, wherein said ion conductor
includes a network modifier.
13. The photonic device of claim 1, further comprising an
insulating layer formed underlying one of said first and said
second electrodes.
14. The photonic device of claim 1, wherein said photonic device is
formed overlying a substrate.
15. The photonic device of claim 14, wherein said substrate
comprises a microelectronic device.
16. The photonic device of claim 15, wherein said photonic device
is electrically coupled to said microelectronic device.
17. A passive display formed using the photonic device of claim
1.
18. An optical switch formed using the photonic device of claim
1.
19. An optical router formed using the photonic device of claim
1.
20. A photonic system comprising: a waveguide formed on a
substrate; and a photonic device including an ion conductor and a
plurality of electrodes, said photonic formed on said substrate and
configured to alter an optical property upon application of an
energy bias across said plurality of electrodes.
21. The photonic system of claim 20, further comprising an
optoelectronic device optically coupled to said waveguide.
Description
FIELD OF THE INVENTION
The present invention generally relates to microelectronic photonic
devices. More particularly, the invention relates to photonic
structures and devices having an optical property that can be
variably altered by manipulating an amount of energy supplied to
the structure.
BACKGROUND OF THE INVENTION
Microelectronic optical or photonic devices and systems including
such devices may be used in a variety of applications. For example,
optical devices are used ill passive displays such as liquid
crystal displays (LCDs), high-definition television displays,
modulators, filters, and the like.
In the case of LCD devices, an image is created by blocking or
allowing transmission of light between a source and a screen or a
display area. In particular, liquid crystal material, in
conjunction with polarizing material and a mirror, is used to alter
the transmission of light based on an applied electric filed. The
applied electric field causes molecules within the liquid crystal
material to align and form a quasi-crystalline structure, which in
turn alters the reflectivity of the material. This change in
reflectivity only persists for so long as the electric field is
applied to the liquid crystal material. Thus, energy must be
supplied to the liquid crystal material to maintain its orientation
even when a displayed image is constant.
Use of liquid crystal material in connection with passive optical
devices may be problematic in several regards. For example, as
noted above, energy must be applied to the liquid crystal material
to maintain information. In addition, the liquid crystal and a
semiconductor circuit for operating the LCD are generally formed on
separate substrates and must be mechanically and electrically
coupled to each other. Coupling devices formed on separate
substrates may be undesirably expensive and time consuming.
Accordingly, improved photonic devices suitable for passive display
applications and systems including the devices are desired.
Other applications where photonic devices are well suited include
optical switches for use with routers in data communication
systems. Presently, routers include optoelectronic components to
convert optical information to electrical signals, components to
filter and amplify the electronic signals, components to rout the
electrical signals, and components to convert the electrical
signals to optical information for further transmission. Use of
electronic components to switch and rout optical information may be
undesirable for several reason. For example, information integrity
may be reduced by the conversion between optical and electrical
signals, and the employment of electronic components may
undesirably add to the cost and complexity of the switch and/or
router. Improved methods and apparatus for switching and routing
optical information are therefore desired.
Photonic devices may also include tunable grating devices for use
as filters. In this case, the photonic device is coupled to a
semiconductor circuit to operate the filter. Forming the photonic
and electronic devices on separates substrate is undesirable for
the reasons noted above. Accordingly, improved methods and
apparatus for forming tunable grating devices and filters are
desired.
SUMMARY OF THE INVENTION
The present invention provides improved photonic devices,
structures, and systems and methods of forming the same. More
particularly, the invention provides photonic structures that have
at least one optical property that can be variably altered upon
application of energy to the structure.
The ways in which the present invention addresses various drawbacks
of now-known photonic devices are discussed in greater detail
below. However, in general, the present invention provides a
structure that can be integrated on a single substrate with a
microelectronic device. In addition, the present invention provides
photonic devices that are relatively easy and inexpensive to
manufacture and that do not require constant application of power
to maintain information.
In accordance with one exemplary embodiment of the present
invention, a photonic structure includes an ion conductor and at
least two electrodes. The structure is configured such that when an
energy bias is applied across the two electrodes, one or more
optical properties of the structure change. In accordance with one
aspect of this embodiment, a transparency of a portion of the
structure changes upon application of a bias across the electrodes.
In accordance with another aspect of this embodiment, reflectivity
of a portion of the structure is altered upon application of a bias
across the electrodes. In accordance with yet a further aspect of
this embodiment, a refractive index of a portion of the structure
is altered upon application of a bias across the electrodes.
In accordance with various embodiments of the invention, an optical
property of a structure can be reversibly altered. In accordance
with one aspect of this embodiment, a photonic structure includes
an ion conductor, a first electrode formed of a soluble material
and a second electrode formed of an inert material. In accordance
with various aspects of this embodiment, the structure also
includes a barrier layer interposed between the ion conductor and
one of the electrodes.
In accordance with further embodiments of the invention, an optical
system includes a photonic structures in accordance with the
present invention and an optoelectronic device (e.g., a light
emitting device or a light detecting device).
In accordance with additional embodiments of the invention, an
optical system includes an optoelectronic device, a waveguide, and
a photonic device.
In accordance with another embodiment of the invention, an optical
switch is formed using a photonic structure of the present
invention. In accordance with one aspect of this embodiment, an
optical router device is formed using the optical switch.
In accordance with another embodiment of the invention, a passive
display device is formed using a photonic structure of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention maybe
derived by referring to the detailed description and claims,
considered in connection with the figures, wherein like reference
numbers refer to similar elements throughout the figures, and:
FIG. 1 is a top plan illustration of a photonic structure formed on
a surface of a substrate in accordance with the present
invention;
FIG. 2 is a cross-sectional illustration of the photonic structure
illustrated in FIG. 1;
FIG. 3 is an illustration of a process of forming a photonic
structure in accordance with an exemplary embodiment of the present
invention;
FIG. 4 is a top plan illustration of a phonic structure array in
accordance with yet another embodiment of the present
invention;
FIG. 5 is a top plan illustration of a photonic structure array in
accordance with another exemplary embodiment of the present
invention;
FIGS. 6 and 7 are schematic illustrations of a photonic system
suitable for use as an optical switch in accordance with an
embodiment of the invention;
FIGS. 8 and 9 are schematic illustrations of a photonic system
suitable for use as an optical switch in accordance with another
embodiment of the invention; and
FIGS. 10 and 11 are schematic illustration of photonic systems,
including a waveguide, in accordance with further embodiments of
the invention.
Skilled artisans will appreciate that elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements in the figures may be exaggerated relative to other
elements to help to improve understanding of embodiments of the
present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The present invention generally relates to photonic structures and
devices and to systems including the structures and devices. More
particularly, the invention relates photonic structures that have a
characteristic that can be altered, and in some cases reversibly
altered, by application of energy such as electricity or light to
the structure.
FIGS. 1 and 2 illustrate a photonic structure 100 formed on a
surface of a substrate 110 in accordance with an exemplary
embodiment of the present invention. As described in more detail
below, structure 100 is configured to change or alter an optical
property upon application of energy to the structure. Although the
applied energy may be in various formed such as radiation, thermal,
and the like, the invention is conveniently described herein in
connection with application of electrical energy to alter an
optical property of a structure.
Exemplary structure 100 includes electrodes 120 and 130, an ion
conductor 140, contacts 150 and 160, and insulating layers 170 and
180. As described in greater detail below, photonic structures in
accordance with the present invention may also include additional
layers such as barrier layers to, for example, facilitate
reversible and reliable operation of the structure.
Generally, structure 100 is configured such that when a bias
greater than a threshold voltage (V.sub.T) is applied across
electrodes 120 and 130, one or more optical properties of structure
100 change. For example, in accordance with one embodiment of the
invention, as a voltage V.gtoreq.V.sub.T is applied across
electrodes 120 and 130, conductive ions within ion conductor 140
begin to migrate and form a region 190, having an increased
concentration of conductive material compared to bulk ion conductor
material, at or near the more negative of electrodes 120 and 130.
Region 190 may form and electrodeposit of solid metal; however,
such an electrodeposit is not required to practice the present
invention.
As region 190 forms the, index of refraction, transparency,
reflectivity, and/or other optical property of region 190 changes.
For example, the transparency of region 190 generally decreases and
reflectivity generally increases as region 190 begins to form.
In the absence of any barriers layers, which are discussed in more
detail below, the threshold voltage required to form region 190
from one electrode toward the other and thereby alter an optical
property of a portion of structure 100 is approximately the redox
potential of the system including ion conductor 140 and electrodes
120 and 130--typically a few hundred millivolts. In accordance with
some embodiments of the invention, if the same voltage is applied
in reverse, region 190 will dissolve back into the ion conductor
and the device will return to an initial state.
A photonic structure may suitably be erased by reversing a bias
applied during a write operation, wherein a magnitude of the
applied bias is equal to or greater than the threshold voltage for
electrodeposition in the reverse direction. In accordance with an
exemplary embodiment of the invention, a sufficient erase voltage
(V.gtoreq.V.sub.T) is applied to structure 100 for a period of
time, which depends on energy supplied during the write operation,
but is typically less than about 1 millisecond to return structure
100 to its original state.
In accordance with various embodiments of the invention, the
volatility of a photonic structure (e.g., structure 100) can be
manipulated by altering an amount of energy (e.g., altering time,
current, voltage, thermal energy, and/or the like) applied during
region 190 growth or a "write" process. In general, the greater the
amount of energy (having a value greater than the threshold energy
for the write process) applied during the write process, the
greater the growth of region 190 and hence the less volatile the
region. Conversely, a relatively volatile region can be formed by
supplying relatively little energy across ion conductor 140. Thus,
relatively volatile photonic devices can be formed using the same
or similar structures used to form nonvolatile devices, and less
energy can be used to form the volatile devices. More volatile
photonic structures may be desirable where fast switching of a
structure is desired--for example, in passive display and/or
switching applications where information is likely to be updated at
a relatively fast rate. The volatile and nonvolatile photonic
structures may be formed on the same substrate and partitioned or
separated from each other such that each partition is dedicated to
either volatile or nonvolatile devices; or, an array of devices may
be configured as volatile or nonvolatile photonic devices using
programming techniques, such that the configuration (i.e., volatile
or nonvolatile) of the device can be altered by changing an amount
of energy supplied during programming the respective portions of
the array.
Referring again to FIGS. 1 and 2, substrate 110 may include any
suitable material. For example, substrate 110 may include
semiconductive, conductive, semiinsulative, insulative material, or
any combination of such materials. In accordance with one
embodiment of the invention, substrate 110 comprises a
semiconductor substrate and includes a micro electronic device 112
formed using a portion of substrate 110. Device 112 may include any
passive or active semiconductor device, such as, for example, light
emitting devices, light detecting devices, drivers, amplifiers,
transistors, or other circuits, devices, or components. If desired,
device 112 may be electrically coupled to an electrode using
electrical connector 114 (e.g., a conductive plug or trace).
Insulating layers 170 and 180 may include any suitable dielectric
or insulating material. For example, layers 170 and 180 may be
formed of silicon oxide, silicon nitride, silicon oxynitride,
polymeric materials such as polyimide or parylene, or any
combination of such materials.
Substrate 110 and ion conductor 114 may be separated by additional
layers (not shown) such as, for example, layers typically used to
form integrated circuits. Because the photonic structures can be
formed over insulating or other materials, the structures of the
present invention are particularly well suited for applications
where substrate (e.g., semiconductor material) space is a premium.
In addition, forming a photonic structure overlying a
microelectronic device may be advantageous because such a
configuration allows greater integration of photonic structures and
microelectronic devices such as device 112.
Electrodes 120 and 130 may be formed of any suitable conductive
material. For example, electrodes 120 and 130 may be formed of
doped polysilicon material or metal. In accordance with one
exemplary embodiment of the invention, one of electrodes 120 and
130 is formed of a material including a metal that dissolves in ion
conductor 140 when a sufficient bias (V.gtoreq.V.sub.T) is applied
across the electrodes (an oxidizable or soluble electrode) and the
other electrode is relatively inert and does not dissolve during
operation of the programmable device (an indifferent or inert
electrode). For example, electrode 120 maybe an anode during a
write process and be comprised of a material including silver that
dissolves in ion conductor 140 and electrode 130 may be a cathode
during the write process and be comprised of an inert material such
as tungsten, nickel, molybdenum, platinum, metal silicides, and the
like. Having at least one electrode formed of a material including
a metal which dissolves in ion conductor 140 facilitates
maintaining a desired dissolved metal concentration within ion
conductor 140, which in turn facilitates rapid and stable region
190 formation within ion conductor 140. Furthermore, use of an
inert material for the other electrode (cathode during a write
operation) facilitates electrodissolution of region 190 and/or
return of the photonic device to an "erased" state after
application of a sufficient voltage.
In cases where only one growth step is contemplated electrodes 120
and 130 may be formed of the same material. In this case, an
optical device is configured for a particular application by use of
an electrical write process that causes growth of region 190, which
alters an optical property of the device. These devices can be use
in optical fiber modules as will as in integrated optoelectronic
systems. The ability to created permanent optical changes in this
manner is useful in, among other things, programmable systems and
self repairing/self-reconfiguring systems that have redundant
element designed to improve the reliability of the systems (e.g.,
buried or underwater network infrastructures, satellites aircrafts,
military applications, and the like). One-time write photonic
structures are relatively easy to fabricate and may be formed using
only a single masking step and one metal deposition and etch step
to form both electrodes 120 and 130, which may both be formed of a
material that dissolves into ion conductor 130 to form region
190.
In accordance with one embodiment of the invention, at least one
electrode 120 and 130 is formed of material suitable for use as an
interconnect metal. For example, electrode 130 may form part of an
interconnect structure within a semiconductor integrated circuit.
In accordance with one aspect of this embodiment, electrode 130 is
formed of a material that is substantially insoluble in material
comprising ion conductor 140. Exemplary materials suitable for both
interconnect and electrode 130 material include metals and
compounds such as tungsten, nickel, molybdenum, platinum, metal
silicides, and the like.
During an erase operation, dissolution of region 190 that may have
formed preferably begins at or near the oxidizable
electrode/electrodeposit interface. Initial dissolution of region
190 at the oxidizable electrode/electrodeposit interface may be
facilitated by forming structure 100 such that the resistance at
the oxidizable electrode/region 190 interface is greater than the
resistance at any other point along the region, particularly, the
interface between region 190 and the indifferent electrode.
One way to achieve relatively low resistance at the indifferent
electrode is to form the electrode of relatively inert,
non-oxidizing material such as platinum. Use of such material
reduces formation of oxides at the interface between ion conductor
140 and the indifferent electrode as well as the formation of
compounds or mixtures of the electrode material and ion conductor
140 material, which typically have a higher resistance than ion
conductor 140 or the electrode material.
Reliable growth and dissolution of region 190 can also be
facilitated by providing a roughened indifferent electrode surface
(e.g., a root mean square roughness of greater than about 1 nm) at
the electrode/ion conductor interface. The roughened surface may be
formed by manipulating film deposition parameters and/or by etching
a portion of one of the electrode of ion conductor surfaces. During
a write operation, relatively high electrical fields form about the
spikes or peaks of the roughened surface, and thus the
electrodeposits are more likely to form about the spikes or peaks.
As a result, more reliable and uniform changes in optical
properties for an applied voltage across electrodes 120 and 130 may
be obtained by providing a roughed interface between the
indifferent electrode (cathode during a write operation) and ion
conductor 140.
Oxidizable electrode material may have a tendency to thermally
dissolve or diffuse into ion conductor 140, particularly during
fabrication and/or operation of structure 100. The thermal
diffusion may be problematic because it may undesirably and
uncontrollably change an optical property during use of structure
100 without a write or erase operation.
To reduce undesired diffusion of oxidizable electrode material into
ion conductor 140 and in accordance with another embodiment of the
invention, the oxidizable electrode includes a metal intercalated
in a transition metal sulfide or selenide material such as A.sub.x
(MB.sub.2).sub.1-x, where A is Ag or Cu, B is S or Se, M is a
transition metal such as Ta, V, and Ti, and x ranges from about 0.1
to about 0.7. The intercalated material mitigates undesired thermal
diffusion of the metal (Ag or Cu) into the ion conductor material,
while allowing the metal to participate in region 190 growth upon
application of a sufficient voltage across electrodes 120 and 130.
For example, when silver is intercalated into a TaS.sub.2 film, the
TaS.sub.2 film can include tip to about 67 atomic percent silver.
The A.sub.x (MB.sub.2).sub.1-x material is preferably amorphous to
prevent undesired diffusion of the metal though the material. The
amorphous material may be formed by, for example, physical vapor
deposition of a target material comprising A.sub.x
(MB.sub.2).sub.1-x.
.alpha.-AgI is another suitable material for the oxidizable
electrode, as well as the indifferent electrode. Similar to the
A.sub.x (MB.sub.2).sub.1-x material discussed above, .alpha.-AgI
can serve as a source of Ag during operation of structure
100--e.g., upon application of a sufficient bias, but the silver in
the AgI material does not readily thermally diffuse into ion
conductor 140. AgI has a relatively low activation energy for
conduction of electricity and does not require doping to achieve
relatively high conductivity. When the oxidizable electrode is
formed of AgI, depletion of silver in the AgI layer may arise
during operation of structure 100, unless excess silver is provided
to the electrode. One way to provide the excess silver is to form a
silver layer adjacent the AgI layer as discussed above in
connection with forming an Ag electrode adjacent ion conductor 140.
The AgI layer reduces thermal diffusion of Ag into ion conductor
140, but does not significantly affect conduction of Ag during
operation of structure 100. In addition, use of AgI increases the
operational efficiency of structure 100 because the AgI mitigates
non-Faradaic conduction (conduction of electrons that do not
participate in the electrochemical reaction).
As noted above, structures in accordance with various embodiments
of the invention optionally include barrier or buffer layers such
as layers 122 and 132. Exemplary materials suitable for buffer
layers 122 and/or 132 include GeO.sub.2 and SiO.sub.x. Amorphous
GeO.sub.2 is relatively porous an will "soak up" silver or other
dissolved conductive material during operation of device 100, but
will retard the thermal diffusion of the conductive material to ion
conductor 140, compared to structures or devices that do not
include a buffer layer. When ion conductor 140 includes germanium,
GeO.sub.2 may be formed by exposing ion conductor 140 to an
oxidizing environment at a temperature of about 300.degree. C. to
about 800.degree. C. or by exposing ion conductor 140 to an
oxidizing environment in the presence of radiation having an energy
greater than the band gap of the ion conductor material. The
GeO.sub.2 may also be deposited using physical vapor deposition
(from a GeO.sub.2 target) or chemical vapor deposition (from
GeH.sub.4 and an O.sub.2).
Buffer layers can also be used to obtain relatively low resistance
at the indifferent electrode by forming a barrier layer between the
oxidizable electrode (anode during a write operation) and the ion
conductor, wherein the barrier layer is formed of material having a
relatively high resistance. Exemplary high resistance materials
include ion conducting materials (e.g., Ag.sub.x O, Ag.sub.x S,
Ag.sub.x Se, Ag.sub.x Te, where x.gtoreq.2, Ag.sub.y I, where
x.gtoreq.1, CuI.sub.2, CuO, CuS, CuSe, CuTe, GeO.sub.2, Ge.sub.z
S.sub.1-z, Ge.sub.z Se.sub.1-z, Ge.sub.z Te.sub.1-z, where z is
greater than or equal to about 0.33), SiO.sub.2, and combinations
of these materials interposed between ion conductor 140 and a metal
layer such as silver.
Buffer layers can also be used to increase a "write voltage" by
placing the buffer layer (e.g., GeO.sub.2 or SiO.sub.x) between ion
conductor 140 and the indifferent electrode. In this case, the
buffer material allows metal such as silver to diffuse though the
buffer and take part in the electrochemical reaction.
Barrier layers 122 and/or 132 may also include a material that
restricts migration of ions between conductor 140 and the
electrodes. In accordance with exemplary embodiments of the
invention, a barrier layer includes conducting material such as
titanium nitride, titanium tungsten, a combination thereof, or the
like. The barrier may be electrically indifferent, i.e., it allows
conduction of electrons through structure 100, but it does not
itself contribute ions to conduction through structure 100. An
electrically indifferent barrier may reduce undesired region 190
growth during operation of the device, and thus may facilitate an
"erase" or dissolution of region 190 when a bias is applied which
is opposite to that used to grow or form the region. In addition,
use of a conducting barrier allows for the "indifferent" electrode
to be formed of oxidizable material because the barrier prevents
diffusion of the electrode material to the ion conductor.
Ion conductor 140 is formed of material that conducts ions upon
application of a sufficient voltage. Suitable materials for ion
conductor 140 include glasses and semiconductor materials. In one
exemplary embodiment of the invention, ion conductor 140 is formed
of chalcogenide material.
Ion conductor 140 may also suitably include dissolved conductive
material. For example, ion conductor 140 may comprise a solid
solution that includes dissolved metals and/or metal ions. In
accordance with one exemplary embodiment of the invention,
conductor 140 includes metal and/or metal ions dissolved in
chalcogenide glass. Exemplary chalcogenide glasses with dissolved
metal suitable for use in forming structure 100 include solid
solutions of As.sub.x S.sub.1-x --Ag, Ge.sub.x Se.sub.1-x --Ag,
Ge.sub.x S.sub.1-x --Ag, As.sub.x S.sub.1-x --Cu, Ge.sub.x
Se.sub.1-x --Cu, Ge.sub.x S.sub.1-x --Cu, Ge.sub.x Te.sub.1-x --Ag
where x ranges from about 0.1 to about 0.5, other chalcogenide
materials including silver, copper, zinc, combinations of these
materials, and the like. In addition, conductor 140 may include
network modifiers that affect mobility of ions through conductor
140. For example, materials such as metals (e.g., silver),
halogens, halides, or hydrogen may be added to conductor 140 to
enhance ion mobility and thus increase erase/write speeds of the
structure.
As discussed in more detail below, in accordance with various
aspects of the invention, ion conductor 140 is preferably
transparent or substantially transparent for the light wavelengths
of interest. In this case, layer 140 is preferable less than or
about equal to 100 .ANG..
A solid solution suitable for use as ion conductor 140 may be
formed in a variety of ways. For example, the solid solution may be
formed by depositing a layer of conductive material such as metal
over an ion conductive material such as chalcogenide glass and
exposing the metal and glass to thermal and/or photo dissolution
processing. In accordance with one exemplary embodiment of the
invention, a solid solution of As.sub.2 S.sub.3 --Ag is formed by
depositing As.sub.2 S.sub.3 onto a substrate, depositing a thin
film of Ag onto the As.sub.2 S.sub.3, and exposing the films to
light having energy greater than the optical gap of the As.sub.2
S.sub.3,--e.g., light having a wavelength of less than about 500
nanometers. If desired, network modifiers may be added to conductor
140 during deposition of conductor 140 (e.g., the modifier is in
the deposited material or present during conductor 140 material
deposition) or after conductor 140 material is deposited (e.g., by
exposing conductor 140 to an atmosphere including the network
modifier).
In accordance with another embodiment of the invention, a solid
solution may be formed by depositing one of the constituents onto a
substrate or another material layer and reacting the first
constituent with a second constituent. For example, germanium
(preferably amorphous) maybe deposited onto a portion of a
substrate and the germanium may be reacted with H.sub.2 Se to form
a Ge--Se glass. Similarly, arsenic can be deposited and reacted
with the H.sub.2 Se gas, or arsenic or germanium can be deposited
and reacted with H.sub.2 S gas. Silver or other metal can then be
added to the glass as described above.
In accordance with one aspect of this embodiment, a solid solution
ion conductor 140 is formed by depositing sufficient metal onto an
ion conductor material such that a portion of the metal can be
dissolved within the ion conductor material and a portion of the
metal remains on a surface of the ion conductor to form an
electrode (e.g., electrode 120). In accordance with alternative
embodiments of the invention, solid solutions containing dissolved
metals maybe directly deposited onto substrate 110 and the
electrode then formed overlying the ion conductor.
An amount of conductive material such as metal dissolved in an ion
conducting material such as chalcogenide may depend on several
factors such as an amount of metal available for dissolution and an
amount of energy applied during the dissolution process. However,
when a sufficient amount of metal and energy are available for
dissolution in chalcogenide material using photodissolution, the
dissolution process is thought to be self limiting, substantially
halting when the metal cations have been reduced to their lowest
oxidation state. In the case of As.sub.2 S.sub.3 --Ag, this occurs
at Ag.sub.4 As.sub.2 S.sub.3 =2Ag.sub.2 S+As.sub.2 S, having a
silver concentration of about 44 atomic percent. If, on the other
hand, the metal is dissolved in the chalcogenide material using
thermal dissolution, a higher atomic percentage of metal in the
solid solution may be obtained, provided a sufficient amount of
metal is available for dissolution.
In accordance with a further embodiment of the invention, the solid
solution is formed by photodissolution to form a macrohomogeneous
ternary compound and additional metal is added to the solution
using thermal diffusion (e.g., in an inert environment at a
temperature of about 85.degree. C. to about 150.degree. C.) to form
a solid solution containing, for example, about 30 to about 50, and
preferably about 34 atomic percent silver. Ion conductors having a
metal concentration above the photodissolution solubility level
facilitates formation of region 190 that is thermally stable at
operating temperatures (typically about 85.degree. C. to about
150.degree. C.) of device 100. Alternatively, the solid solution
may be formed by thermally dissolving the metal into the ion
conductor at the temperature noted above; however, solid solutions
formed exclusively from photodissolution are thought to be less
homogeneous than films having similar metal concentrations formed
using photodissolution and thermal dissolution.
Ion conductor 140 may also include a filler material, which fills
interstices or voids. Suitable filler materials include
non-oxidizable and non-silver based materials such as a
non-conducting, immiscible silicon oxide and/or silicon nitride,
having a cross-sectional dimension of less than about 1 nm, which
do not contribute to the growth of an electrodeposit. In this case,
the filler material is present in the ion conductor at a volume
percent of up to about 5 percent to reduce a likelihood that an
electrodeposit will spontaneously dissolve into the supporting
ternary material as the device is exposed to elevated temperature,
which leads to more stable device operation without compromising
the performance of the device. Ion conductor 140 may also include
filler material to reduce an effective cross-sectional area of the
ion conductor. In this case, the concentration of the filler
material, which may be the same filler material described above but
having a cross-sectional dimension up to about 50 nm and be present
in the ion conductor material at a concentration of up to about 50
percent by volume. The filler material may also include metal such
as silver or copper to fill the voids in the ion conductor
material.
In accordance with one exemplary embodiment of the invention, ion
conductor 140 includes a germanium-selenide glass with silver
diffused in the glass. Germanium selenide materials are typically
formed from selenium and Ge(Se).sub.4/2 tetrahedra that may combine
in a variety of ways. In a Se-rich region, Ge is 4-fold coordinated
and Se is 2-fold coordinated, which means that a glass composition
near Ge.sub.0.20 Se.sub.0.80 will have a mean coordination number
of about 2.4. Glass with this coordination number is considered by
constraint counting theory to be optimally constrained and hence
very stable with respect to devitrification. The network in such a
glass is known to self-organize and become stress-free, making it
easy for any additive, e.g., silver, to finely disperse and form a
mixed-glass solid solution. Accordingly, in accordance with one
embodiment of the invention, ion conductor 140 includes a glass
having a composition of Ge.sub.0.17 Se.sub.0.83 to Ge.sub.0.25
Se.sub.0.75.
The composition and structure of ion conductor 140 material often
depends on the starting or target material used to form the
conductor. Generally, it is desired to form a homogenous material
layer with low oxygen content for conductor 140 to facilitate
reliable and repeatable device performance.
Contacts 150 and 160 may suitably be electrically coupled to one or
more electrodes 120, 130 to facilitate forming electrical contact
to the respective electrode. Contacts 150 and 160 may be formed of
any conductive material and are preferably formed of a metal,
alloy, or composition including aluminum, tungsten, or copper.
FIG. 3 illustrates a process for forming a photonic structure, such
as structure 100, in accordance with the present invention. Process
300 begins with providing a substrate (step 302). As noted above,
the substrate may include semiconductor material having a devices
formed using the substrate material. To isolate the substrate from
the photonic device, an insulating layer (e.g., layer 170) is
formed overlying the substrate (step 304). Next, ion conductor 140
is formed by depositing ion conducting material as described above
and using a suitable mask and etch process to form the conductor in
a desired pattern (step 306). Process 300 optionally includes the
step of forming barrier layers such as layers 122 and 132 described
above. The barrier layers may be formed by, for example, depositing
a suitable barrier material, patterning the barrier material, and
etching the material to form the desired pattern of electrodes
(step 308). Electrodes 120 and 130 may similarly be formed by
depositing a layer of electrode material, patterning the electrode
material, and etching the material to form the electrodes (step
310). As noted above, photonic structures in accordance with the
present invention may include electrodes formed of different
material. In this case, the electrode formation step may comprise
two sub-steps: one to form each electrode. Once electrodes 120 and
130 are formed, insulating or isolating layer 180 and contacts 150
are formed (steps 312 and 314), using, for example the deposition
and etch technique described above, damascene techniques, or other
suitable processes. Further, as illustrated in FIG. 9, a substrate
etch may be used to facilitate light transmission through ion
conductor 140.
FIGS. 4 and 5 illustrate top plan views of arrays 400 and 500 of
photonic structures, suitable for passive display and similar
applications, in accordance with exemplary embodiments of the
invention. Although the arrays are illustrated with square or
rectangular structures and with a specific number of structures,
any suitable geometric shape and/or number of structures may be
used to form an array in accordance with the present invention.
As illustrated in FIG. 4, array 400 includes a plurality of
independently accessible structures 402, which may be variably,
optically altered, and which may be reversibly altered, as
described above. As illustrated in FIG. 4, upon application of
energy across electrodes 408 and 410, some of the photonic
structures 402 become altered such that an optical property
partially changes (illustrated as element 404), such that cell 404
is partially reflective or opaque, and may be further altered to
form cells 406, which may be completely or substantially completely
reflective or opaque in the light wavelengths of interest. Use of
multiple photonic devices in an array allows for gray scale images,
which may be formed by: altering a portion of devices 402 or
partially altering a portion or all of devices 402.
Array 500 is similar to array 400, except array 500 includes
elongated structures 502, including electrodes 508 and 510. Optical
properties of structures 502 are altered by applying a bias across
the electrodes to form partially opaque or reflective structure 504
or substantially completely reflective structure 506.
FIGS. 6-9 illustrate optoelectronic systems, suitable for optical
switching applications, in accordance with various embodiments of
the present invention. In particular, FIGS. 6 and 7 illustrate a
system 600, including a photonic structure 602, a light emitting
device 604, and light detecting device 606 and 608. Light emitting
devices may include, for example, light emitting diodes or lasers
such as vertical cavity surface emitting laser or edge emitting
lasers, or the like; light detecting devices may include photo
diode or the like.
In operation, system 600 can switch or route optical signals to
devices 606 and 608 by altering the optical properties (e.g.,
refractive index and/or reflectivity) of a portion of structure 602
(e.g., an ion conductor region 608 of structure 602) such that the
reflection angle of light emitted from device 604 changes and the
light is transmitted to the desired light receiving device 606 or
608. More particularly, upon application of a bias (having energy
greater than the threshold energy for oxidation) across electrodes
612 and 614, metal from one of the electrodes (e.g., electrode 612)
dissolves into ion conductor 610 to alter the optical properties of
region 610. For example, a region 616 of concentrated conductive
material, which has a higher reflectivity than bulk conductor 610
material, forms upon application of a sufficient bias. In
accordance with aspect of this embodiment of the invention,
electrode 614 is formed of material such as indium tin oxide, which
is substantially transparent in at least one wavelength of light
transmitted between device 604 and device 606 or 608.
Alternatively, the structure may include an aperture through the
top electrode to allow light transmission through to conductor 610
and also allow application of a bias across the electrodes.
FIGS. 8 and 9 illustrate a system 800, which includes a photonic
structure 802, a light emitting device 804 and light detecting
devices 806 and 808, which are formed on opposite sides of
structure 802.
Structure 800 operates in a manner similar to structure 600,
namely, that upon application of a sufficient bias across
electrodes 812 and 814, an optical property of bulk ion conductor
material 810 is altered, by forming a region 816, to select one of
output devices 806 and 808.
FIGS. 10 and 11 illustrate additional systems 1000 and 1100 in
accordance with the present invention. Systems 1000 and 1100 are
similar to systems 600 and 800, except one or more of the
optoelectronic devices of system 600 and 800 are replaced by a
waveguide. Although not illustrated in the drawing figures,
additional systems of the present invention include both a
waveguide and one or more optoelectronic devices.
System 1000 includes a photonic structure 1002, including
electrodes 1004 and 1006 and an ion conductor 1008, and waveguide
1010. Electrodes 1004 and 1006 and ion conductor material 1008
maybe selected from any of the material described above in
connection with structure 100. In addition, system 1000 may include
various buffer and/or barrier layers as described above. Waveguide
1010 maybe formed of any suitable waveguide material (e.g., silicon
oxide) and may include suitable cladding layers (not
illustrated).
In operation, light is transmitted to or from waveguide 1010, and
may be deflected to an optoelectronic device of another waveguide
by altering the optical properties by growing a region 1012, having
a higher concentration of conductive material compared to bulk
conductor material 1008.
Structure 1100, illustrated in FIG. 11, includes a photonic
structure 1102, having electrodes 1106 and 1108 and ion conductor
material 1108. Structure 1102 may be formed of any of the material
described above in connection with structure 1000, and structure
1100 operates in a manner similar to structure 1000.
Although the present invention is set forth herein in the context
of the appended drawing figures, it should be appreciated that the
invention is not limited to the specific form shown. For example,
although the photonic structures of the present invention are
described in connection with passive devices and optical switches,
the application is so limited. Various other modifications,
variations, and enhancements in the design and arrangement of the
method and apparatus set forth herein, may be made without
departing from the spirit and scope of the present invention as set
forth in the appended claims.
* * * * *